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HLGEM
HLGEM
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The join syntax replaced the old comma syntax in 1992. There is currently no reason to ever write code with the comma syntax. You gain nothing and you are subject to some problems you simply don't have with explicit syntax. 

In the first place as you get more complicated queries is very easy to do an accidental cross join by missing a where condition. This is something the explicit join syntax can prevent from happening as you will get a syntax error. 

If you intend a cross join, the explicit join syntax will make that clear while in the implicit syntax someone doing maintenance may assume you forgot to add the where clause. 

Then there is the problem of left and right joins which are problematic in at least some dbs using the implicit syntax. They are deprecated in SQL Server and in fact do not return correct results realiably even in the older versions. No query that needs an outer join should contain the implicit syntax in SQL Server. Further

Further, I have seen questions here and on other sites where wrong results happened when people mix the implicit and explicit joins (when adding a left join for instance), so it is a poor idea to mix them. 

Finally many people who use implicit joins don't actually understand joins. This is a critical understanding you must have to effectively query a database.

The join syntax replaced the old comma syntax in 1992. There is currently no reason to ever write code with the comma syntax. You gain nothing and you are subject to some problems you simply don't have with explicit syntax. In the first place as you get more complicated queries is very easy to do an accidental cross join by missing a where condition. This is something the explicit join syntax can prevent from happening as you will get a syntax error. If you intend a cross join, the explicit join syntax will make that clear while in the implicit syntax someone doing maintenance may assume you forgot to add the where clause. Then there is the problem of left and right joins which are problematic in at least some dbs using the implicit syntax. They are deprecated in SQL Server and in fact do not return correct results realiably even in the older versions. No query that needs an outer join should contain the implicit syntax in SQL Server. Further, I have seen questions here and on other sites where wrong results happened when people mix the implicit and explicit joins (when adding a left join for instance), so it is a poor idea to mix them. Finally many people who use implicit joins don't actually understand joins. This is a critical understanding you must have to effectively query a database.

The join syntax replaced the old comma syntax in 1992. There is currently no reason to ever write code with the comma syntax. You gain nothing and you are subject to some problems you simply don't have with explicit syntax. 

In the first place as you get more complicated queries is very easy to do an accidental cross join by missing a where condition. This is something the explicit join syntax can prevent from happening as you will get a syntax error. 

If you intend a cross join, the explicit join syntax will make that clear while in the implicit syntax someone doing maintenance may assume you forgot to add the where clause. 

Then there is the problem of left and right joins which are problematic in at least some dbs using the implicit syntax. They are deprecated in SQL Server and in fact do not return correct results realiably even in the older versions. No query that needs an outer join should contain the implicit syntax in SQL Server.

Further, I have seen questions here and on other sites where wrong results happened when people mix the implicit and explicit joins (when adding a left join for instance), so it is a poor idea to mix them. 

Finally many people who use implicit joins don't actually understand joins. This is a critical understanding you must have to effectively query a database.

Source Link
HLGEM
HLGEM
  • 28.8k
  • 4
  • 69
  • 116

The join syntax replaced the old comma syntax in 1992. There is currently no reason to ever write code with the comma syntax. You gain nothing and you are subject to some problems you simply don't have with explicit syntax. In the first place as you get more complicated queries is very easy to do an accidental cross join by missing a where condition. This is something the explicit join syntax can prevent from happening as you will get a syntax error. If you intend a cross join, the explicit join syntax will make that clear while in the implicit syntax someone doing maintenance may assume you forgot to add the where clause. Then there is the problem of left and right joins which are problematic in at least some dbs using the implicit syntax. They are deprecated in SQL Server and in fact do not return correct results realiably even in the older versions. No query that needs an outer join should contain the implicit syntax in SQL Server. Further, I have seen questions here and on other sites where wrong results happened when people mix the implicit and explicit joins (when adding a left join for instance), so it is a poor idea to mix them. Finally many people who use implicit joins don't actually understand joins. This is a critical understanding you must have to effectively query a database.